The Prince of Wales and the Duchess of Cornwall have arrived in Philadelphia for a two-day official visit to the US.
Prince Charles and Camilla will collect the prize in New York
They will visit Independence Hall, where the Declaration of Independence was adopted and the US Constitution drafted, and see the Liberty Bell.
Prince Charles will also accept an award for his environmental work, but has been criticised by some campaigners for flying to accept it in person.
The couple travelled from London on a scheduled British Airways flight.
The flight on Friday was delayed by an hour and, as the Boeing 777 waited on the tarmac, the captain told passengers: "We seem to have been caught up in rush hour traffic at Heathrow."
But the flight made good time and Prince Charles and Camilla arrived in Philadelphia, where temperatures were -6C, five minutes early.
During their visit to the city, the couple will be shown one of 2,700 murals which resulted from an anti-graffiti drive and bid to revitalise rundown areas which began in the 1980s.
In New York on Sunday they will visit the Harlem Children's Zone, which helps disadvantaged children.
That evening the prince is set to collect the 10th Anniversary Global Environmental Citizen Award.
Prince Charles has been awarded the prize by the Centre for Health and Global Environment at Harvard Medical School for "his outstanding work towards protecting the environment".
Actress Meryl Streep and previous winner Al Gore, the former US vice- president, will present the award.
However, Prince Charles has been criticised by some green campaigners for deciding to fly to the US to collect the award.
Environmental campaigners Plane Stupid, which campaign against aircraft carbon emissions, accused the prince of "green hypocrisy".
Meanwhile, Environment Secretary David Miliband has suggested Prince Charles should receive the prize via video-link up rather than make the 7,000 mile round-trip.
The royal couple normally fly by a private charter plane and the decision to use a scheduled flight follows an announcement by Clarence House last month to make the royal household's travel more eco-friendly. Aides said scheduled flights would be used when security permitted it.
In the summer, aides to the prince are set to publish details of his carbon footprint in his annual accounts, as well as set a target to substantially reduces the carbon emissions of his office and household.
Clarence House was unable to confirm the last time Prince Charles used a commercial flight for an official royal visit.
"He hasn't flown scheduled for a number of years. It's certainly significant," a spokesman said.